Electron irradiation damage in stoichiometric and substoichiometric tantalum carbides TaCxpart 1: Thershold displacement energies

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Abstract
The damage rate (electrical resistivity increase per fluence unit δρ/δΦ) has been measured in cubic tantalum carbides TaC0.99 and TaC0.80, during irradiation at 21 K by electrons of energies E ranging from 0.4 to 2.7 MeV. Both experimental δρ/δΦ versus E curves clearly display two thresholds at E < 0.35 MeV and E < 1.5 MeV. Comparison with theoretical displacement cross-sections calculated for TaC allowed us to attribute unambiguously the first threshold to carbon displacements and the second one to tantalum. Surprisingly, in the largely substoichiometric TaC0.80 sample, irradiation still creates carbon Frenkel pair type defects. Taking into account the real irradiation conditions, the deduced parameters are TC d = 28 ± 6eV and Td Ta = 42 ± 2eV for the threshold displacement energies in TaC0.99 (resp. 28 ± 6 and 32 ± 2eV in TaC0.80), and ρC F = 26 ± 5 μΩ-cm/at.%. for the specific mean resistivity of carbon Frenkel pair in TaC0·99.